This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present technology. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present technology. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
Gas production from hydrocarbon reservoirs is often associated with liquid production. The produced liquids may be reservoir formation water or condensed hydrocarbon gas. During the early life of a gas well, the gas production rate is sufficient to carry produced liquid to the surface. As the reservoir pressure is depleted with continuous production, the gas production rate will eventually decrease to a point where the produced liquids can no longer be carried by gas flow out of the wellbore. As a result, the produced liquid starts to accumulate at the bottom of the well, which is called liquid loading.
Liquid loading is a common and challenging problem in gas well operations, particularly in the later life of wells. Removal of liquid, in many instances water, out of the gas well becomes important to maintain gas production and keep the well flowing. This can be accomplished by various kinds of artificial lift methods and systems. Plunger lift methods and systems are generally considered the most cost effective artificial lift approaches in the industry today.
Many conventional plunger lift systems consist of a plunger, well production tubing, a bottom hole assembly that includes tubing stopper and bumper spring, and wellhead equipment that includes plunger catcher, lubricator, flow outlet, valves, and control device. The plunger is a cylindrical device used in the tubing and it is designed to seal against the interior of the tubing while it moves freely inside the tubing string. In a typical plunger lift operation, the well is shut-in so that the plunger can descend to the bottom of the well below the accumulated continuous liquid column; after sufficient wellbore pressure has built up, the well valve is opened; the wellbore pressure pushes the plunger and, consequently, the column of liquid on top of plunger up the well all the way to surface; when reaching the surface, the plunger is held at the wellhead to allow the gas to flow for as long as the well permits; then the plunger is released into the well again for a new cycle of plunger lift operation.
The well shut-in requirement during plunger descent is one of the major disadvantages for conventional plunger lift technology. This limitation restricts the use of the technology for high rate wells because of the unaffordable production loss. Because of the hourly, periodic wellbore operation switches, a wellhead surface control system, usually comprising an electronic control panel, a power supply (for remote wells, a solar panel is very common), and pneumatic flow-control valves, becomes essential.
Continuous flow plungers such as those described in U.S. Pat. No. 6,209,637, U.S. Pat. No. 6,644,399, and U.S. Pat. No. 7,243,730 attempt to address the well shut-in time problem. However, each of the devices and methods disclosed in these patents requires a surface control device. Surface control devices keep the cost high for plunger operations. While providing flexibility or options for optimizing plunger lift operations, the surface control system typically accounts for more than 80% of the total capital expense of a plunger lift system installation. In addition, none of the current plungers are applicable in high rate gas producing wells and none of them appear to utilize improved hydrodynamics.
Field experiences have shown that continuous flow plungers have difficulty reaching the tubing bottom in high flow rate wells. This may be due to a lack of sufficient mass, an inability to overcome hydrodynamic forces such as pressure and drag caused by continuous water, or another design limitation.
What is needed are more efficient and effective plunger lift systems and methods for artificially lifting liquids out of gas wells that can operate with or without surface control equipment and operate in high rate gas producing wells.